Compositions and methods for forming articles having silver metal

ABSTRACT

Electrically-conductive silver metal can be provided in a thin film or pattern on a substrate from a silver complex having reducing silver ions and represented by:
 
(Ag + ) a (L) b (P) c    (I)
 
wherein L represents an α-oxy carboxylate; P represents a 5- or 6-membered N-heteroaromatic compound; a is 1 or 2; b is 1 or 2; and c is 1, 2, 3, or 4, provided that when a is 1, b is 1, and when a is 2, b is 2. The silver complex is mixed in a hydroxy-free, nitrile-containing aprotic solvent with a polymer that is either (i) a hydroxy-containing cellulosic polymer or (ii) a non-cellulosic acrylic polymer having a halo- or hydroxy-containing side chain. The reducible silver ions in the a thermally sensitive thin film or pattern can be thermally converted to electrically-conductive metallic silver under suitable heating conditions to provide a product article that can be used in various devices.

RELATED APPLICATIONS

Reference is made to the following commonly assigned and copendingpatent applications, the disclosures of all of which are incorporatedherein by reference:

U.S. Ser. No. 15/231,804 (filed on Aug. 9, 2016 by Shukla);

U.S. Ser. No. 15/231,811 (filed on Aug. 9, 2016 by Shukla);

U.S. Ser. No. 15/231,817 (filed on Aug. 9, 2016 by Shukla, Mis, Welter,Klubek, and Donovan);

U.S. Ser. No. 15/231,823 (filed on Aug. 9, 2016 by Shukla);

U.S. Ser. No. 15/231,837 (filed on Aug. 9, 2016 by Shukla), recentlyallowed;

U.S. Ser. No. 15/231,847 (filed on Aug. 9, 2016 by Shukla);

U.S. Ser. No. 15/231,852 (filed on Aug. 9, 2016 by Shukla, Lenhard, Mis,and Donovan);

U.S. Ser. No. 15/213,857 (filed on Aug. 9, 2016 by Shukla, Mis, Welter,and Donovan);

U.S. Ser. No. 15/456,827 (filed on Mar. 13, 2017 by Shukla, Donovan, andGilimor);

U.S. Ser. No. 15/456,868 (filed on Mar. 13, 2017 by Shukla and Donovan);

U.S. Ser. No. 15/456,686 (filed on Mar. 13, 2017 by Shukla and Donovan);and

U.S. Ser. No. 15/622,172 filed on Jun. 14, 2017, by Shukla, Donovan, andMeyer.

FIELD OF THE INVENTION

This invention relates to methods that utilize thermally sensitivenon-aqueous precursor compositions containing a silver complex havingreducible silver ions, a hydroxy-free, nitrile-containing aproticsolvent, and a specific type of polymer to provideelectrically-conductive metallic silver upon suitable application ofheat to reduce the reducible silver ions. Articles withelectrically-conductive metallic silver thin films or patterns on asubstrate can be provided. Each complex includes one or more reduciblesilver ions complexed with an α-oxy carboxylate and one or more 5- or6-membered N-heteroaromatic compounds.

BACKGROUND OF THE INVENTION

It is well known that silver as a precious metal has desirableelectrical and thermal conductivity, catalytic properties, andantimicrobial behavior. Thus, silver and silver-containing compoundshave been widely used in alloys, metal plating processes, electronicdevices, imaging sciences, medicine, clothing or other fibrousmaterials, and other commercial and industrial articles and processes totake advantage of silver's beneficial properties.

For example, silver compounds or silver metal have been described foruse as metallic patterns or electrodes in metal wiring patterns, printedcircuit boards (PCBs), flexible printed circuit boards (FPCs), antennasfor radio frequency identification (RFID) tags, plasma display panels(PDPs), liquid crystal displays (LCDs), organic light emitting diodes(OLEDs), flexible displays and organic thin film transistors (OTFTs),among other electronic devices known in the art.

Rapid advances are also occurring for making and using variouselectronic devices for various communication, financial, and archivalpurposes.

Silver is an ideal conductor having electrical conductivity 50 to 100times greater than indium tin oxide that is commonly used today in manydevices. For example, the art has described the preparation ofelectrically-conductive films by forming and developing (reducing) asilver halide image in “photographic” silver halide emulsions through anappropriate mask to form electrically-conductive grid networks havingsilver wires having average sizes (width and height) of less than 10 μmand having appropriate lengths. Various efforts have been made to designthe silver halide emulsions and processing conditions to optimizeelectrically-conductive grid designs.

While silver as an electrical conductor has a wide range of potentialuses in the field of printed electronics, the microfabrication ofelectrically-conductive tracks (grids, wires, or patterns) byphotolithographic and electroless techniques is time consuming andexpensive, and there is an industrial need for direct digital printingto simplify the processes and to reduce manufacturing costs.

Furthermore, it is desirable to fabricate silver-containing electronicsonto polymeric or similar temperature-sensitive substrates bysolution-based printing processes. Metallic electrically-conductivewires or grids of low resistance must be achieved at sufficiently lowtemperatures so as to be compatible with organic electronics onpolymeric substrates. Among various known methods for fabricatingelectrically-conductive silver grids or patterns, the direct printing ofsilver-containing inks provides attractive prospects for making suchelectrically-conductive patterns.

Commonly used silver-conductive inks useful for this purpose arecurrently based or dependent upon the presence of silver nanoparticle(NP) solutions or dispersions, all of which have associated drawbacks.To overcome the common problem of aggregation and flocculation in silvernanoparticle based inks, various thiolate encapsulating surfactants ordispersants can be used. Volkman et al. [Chem. Mater. 23, 4634-4640(2011)] observed that a thiolate encapsulating surfactant could be usedto treat 3 nm silver particles in silver-containing inks to achievefilms sintered at temperatures above 175° C. in air. Sintering isessential to obtain the electrical conductivities required forelectronic applications. The effects of sintering on electricalperformance and microstructure for an inkjet-printed copper nanoparticleink were explored by Niittynen et al. [Sci. Rep. 5, 8832 (2015)]. Theseworkers used laser and intense pulsed light (IPL) sintering in order toobtain articles having electrical conductivities greater than 20% ofthat of bulk copper.

However, sintering techniques have major disadvantages. In many cases,sintering steps require high temperatures that are not compatible withpolymer substrates such as polyethylene terephthalate or polycarbonatethat are commonly employed in many consumer electronic articles.Furthermore, the metal-containing inks used for these processes havedisparate viscosities and synthetic parameters. Particle-based inkstypically contain electrically-conductive metal particles that aresynthesized separately and then incorporated into an ink formulation.Each resulting particle-based ink must then be optimized for use in aspecific printing process.

Grouchko et al. [ACS Nano 5(4) 3354-3359 (2011)] recently overcame someof these problems by employing a room temperature, “built in” sinteringmechanism that successfully produced silver metal articles exhibitingelectrical conductivities as high as 41% of the electrical conductivityof bulk silver. To obtain these electrical conductivity values, achloride salt (such as NaCl) or HCl vapor was employed to strip apolymeric (polyacrylic acid sodium salt) electrosterically stabilizingcoating from the ˜15 nm diameter silver nanoparticle feedstock. Thissintering mechanism consisted of spontaneous coalescence and Ostwaldripening, driven by the surface-to-volume energy of the very smallsilver nanoparticles. Thus, all of these nanoparticle-based processesinherently involve sintering processes, whether they are chemical (forexample using a strong acid such as hydrochloric acid), thermal, laser,or UV activated.

Inkjet printing and flexographic printing have also been proposed forproviding patterns of silver or silver-containing compounds, requiringthe careful fabrication of a silver-containing paste or “ink” withdesirable surface tension, viscosity, stability, and other physicalproperties required for such application processes. High silver contenthas generally been required for high electrical conductivity, andcalcination or sintering may be additionally required for increasingelectrical conductivity of printed silver inks.

An alternative to the approaches described above is to employ a chemicalink formulation where the silver source is a molecular precursor orcation (such as a silver salt) that is then chemically reacted (orreduced) to produce silver metal. Electrically-conductive inks that arein the form of a chemical solution rather than as a suspension ordispersion of metal particles, have gained interest in recent years[see, for example, Walker and Lewis in J. Am. Chem. Soc. 134, 1419(2012); and Jahn et al. Chem. Mater. 22, 3067-3071 (2010)]. Oneconductive ink of this type is known as a Metalorganic Decomposition(MOD) variety ink, for example, as described by Jahn et al. [Chem.Mater. 22, 3067-3071 (2010)] who investigated silver printing using anaqueous transition metal complex [AgO₂C(CH₂OCH₂)₃H]-containing MOD ink.They reported the formation of metallic silver features havingelectrical conductivities as high as 2.7×10⁷ S m⁻¹, which corresponds toan electrical conductivity that is 43% of that of bulk silver, althougha sintering temperature of 250° C. was required. MOD inks thus overcomesome problems associated with the use of nanoparticle-containing inks,for example, nozzle clogging, but numerous printing passes are generallyrequired to obtain an adequate sheet resistance. Post-treatmentsintering processes are also still required to fully consolidate theelectrically-conductive articles if the growth process is initiated fromdiscrete nanoparticle intermediates, which is common in MOD inkprocesses.

U.S. Patent Application Publication 2015/0004325 (Walker et al.)describes a chemically-reactive silver ink composition comprised of acomplex of a silver carboxylate salt and an alkylamine, in which thecomplex is used to form an electrically-conductive silver structure at atemperature of 120° C. or less. Unfortunately, even these temperaturesrender the ink incompatible with many polymeric and paper substratesused in flexible electronic and biomedical devices. Furthermore, sincealkylamines are known to reduce silver at room temperature, long termstability of such compositions is tentative. The complexes must be keptin air-tight refrigerated storage for extended keeping stability (ColumnI, paragraph 0054 of the publication). Furthermore, the publicationteaches long heating times were needed to obtain low resistivity in theresulting articles.

A common coordinating ion to form organic silver complexes is carboxylicacid [Prog. Inorg. Chem., 10, 233 (1968)]. However, silver-carboxylatecomplexes are generally insoluble in organic solvents [see, for example,U.S. Pat. No. 5,491,059 of Whitcomb and U.S. Pat. No. 5,534,312 of Hillet al.] and have a high decomposition temperature. To solve thisproblem, several methods have been proposed for example, in Ang. Chem.,Int. Ed. Engl., 31, p. 770 (1992), Chem. Vapor Deposition, 7, 111(2001), Chem. Mater., 16, 2021 (2004), and U.S. Pat. No. 5,705,661(Iwakura et al.). Among such methods are those using silver carboxylateshaving long alkyl chains or including amine compounds or phosphinecompounds. However, the silver complexes known thus far haveinsufficient stability or solubility and a high decompositiontemperature is needed for pattern formation and are decomposed slowly.

Allegedly to address some of these problems, U.S. Pat. No. 8,226,755(Chung et al.) describes silver complexes formed by reacting a silvercompound (such as a silver salt) with an ammonium carbamate compound orammonium carbonate compound. Moreover, U.S. Patent ApplicationPublication 2010/0021704 (Yoon et al.) describes the preparation and useof fatty acid silver salts complexed with amines and in admixture withsilver oxide to form silver metal from the silver oxide at lowtemperature.

U.S. Pat. No. 8,163,073 (Chan et al.) describes the use of silverammonium complex ions, silver amine complex ions, silver-amino acidcomplex ions, silver halide complex ions, silver sulfite complex ions,or silver thiosulfate complex ions for silver plating processes to formsilver wires for various devices.

U.S. Pat. No. 7,682,774 (Kim et al.) describes other photosensitivecompositions comprising silver fluoride-organic complex precursors ascatalyst precursors as well as the use of polymer derived from a monomerhaving a carboxyl group and a co-polymerizable monomer that may providepolymeric stability and developability of the resulting “seed” silvercatalyst particles used for electroless plating.

U.S. Pat. No. 8,419,822 (Li) describes a process for producingcarboxylic acid-stabilized silver nanoparticles by heating a mixture ofa silver salt, a carboxylic acid, and a tertiary amine. However, it hasbeen observed that such silver-containing complexes are not thermally orlight stable. The reducible silver ions are readily reduced underambient light conditions, and the resulting electrical conductivity ofsilver particles is minimal.

Other industrial approaches to preparing electrically-conductive filmsor elements have been directed to formulating and applying photocurablecompositions containing dispersions of metal particles such as silvermetal particles to substrates, followed by curing of the photocurablecomponents in the photocurable compositions. The applied silverparticles in the cured compositions thus act as catalytic (seed)particles for electrolessly plated electrically-conductive metals.Useful electrically-conductive grids prepared in this manner aredescribed for example, in U.S. Pat. No. 9,188,861 (Shukla et al.) andU.S. Pat. No. 9,207,533 (Shukla et al.) and in U.S. Patent ApplicationPublications 2014/0071356 (Petcavich) and 2015/0125596 (Ramakrishnan etal.). Using these methods, photocurable compositions containingcatalytic silver particles can be printed and cured on a suitabletransparent substrate, for example, a continuous roll of a transparentpolyester, and then electroless plating can be carried out on thecatalytic silver particles. However, these methods require that highquantities of silver particles be dispersed within the photocurablecompositions in a uniform manner so that coatings or printed patternshave a sufficiently high concentration of catalytic sites. Withouteffective dispersing, silver particles readily agglomerate, leading toless effective and uniform application of catalytic metal patterns andelectroless plating.

Despite the various approaches and efforts to provideelectrically-conductive silver in various consumer and industrialarticles described above, there remains a need for thermally sensitivesilver-generating compositions and processes which can rapidly generatemetallic silver under appropriate heating conditions. Ideally, suchthermally sensitive compositions should have several properties:stability at room temperature for an extended time (that is, limitedself-reduction of silver ions); capability of being deposited using awide range of application processes, whether uniformly or patternwise;useful at room temperature; and controllable chemical activity.

SUMMARY OF THE INVENTION

The present application provides a non-aqueous precursor compositionconsisting essentially of:

(a) a silver complex comprising one or more reducible silver ionscomplexed with an α-oxy carboxylate and a 5- or 6-memberedN-heteroaromatic compound, the silver complex being represented by thefollowing formula (I):(Ag⁺)_(a)(L)_(b)(P)_(c)   (I)wherein L represents the α-oxy carboxylate; P represents the 5- or6-membered N-heteroaromatic compound; a is 1 or 2; b is 1 or 2; and c is1, 2, 3, or 4, provided that when a is 1, b is 1, and when a is 2, b is2;

(b) a hydroxy-free, nitrile-containing aprotic solvent having a boilingpoint at atmospheric pressure of at least 100° C. and less than 500° C.;and

(c) a polymer that is either (i) a hydroxy-containing cellulosic polymeror (ii) a non-cellulosic acrylic polymer having a halo- orhydroxy-containing side chain, which polymer is present in an amount ofat least 0.25 weight % and up to and including 15 weight %, based on thetotal weight of reducible silver ions in the silver complex.

This invention also comprises a method for providing silver metal,comprising:

providing a thermally sensitive thin film or a thermally sensitive thinfilm pattern on a substrate, the thermally sensitive thin film orthermally sensitive thin film pattern, consisting essentially of:

(a) a silver complex comprising one or more reducible silver ionscomplexed with an α-oxy carboxylate and a 5- or 6-memberedN-heteroaromatic compound,

the silver complex being represented by the following formula (I):(Ag⁺)_(a)(L)_(b)(P)_(c)   (I)wherein L represents the α-oxy carboxylate; P represents the 5- or6-membered N-heteroaromatic compound; a is 1 or 2; b is 1 or 2; and c is1, 2, 3, or 4, provided that when a is 1, b is 1, and when a is 2, b is2;

(b) a hydroxy-free, nitrile-containing aprotic solvent having a boilingpoint at atmospheric pressure of at least 100° C. and less than 500° C.;and

(c) a polymer that is either (i) a hydroxy-containing cellulosic polymeror (ii) a non-cellulosic acrylic polymer having a halo- orhydroxy-containing side chain, which polymer is present in an amount ofat least 0.25 weight % and up to and including 10 weight %, based on thetotal weight of reducible silver ions in the silver complex; and

thermally converting reducible silver ions in the thermally sensitivethin film or thermally sensitive thin film pattern toelectrically-conductive silver metal by heating the thermally sensitivethin film or thermally sensitive thin film pattern at a temperature thatis at or below the glass transition temperature of the silver complexfor a time sufficient to convert at least 95 mol % of the reduciblesilver ions in the silver complex to silver metal, to provide anelectrically-conductive silver metal-containing thin film orelectrically-conductive silver metal-containing thin film pattern on thesubstrate,

wherein the electrically-conductive silver metal-containing thin film orelectrically-conductive silver metal-containing thin film patternconsists essentially of:

silver metal;

the α-oxy carboxylate;

the 5- or 6-membered N-heteroaromatic compound; and

either (i) the hydroxy-containing cellulosic polymer or (ii) thenon-cellulosic acrylic polymer having a halo- or hydroxy-containing sidechain.

Further, a method of this invention for providing two or moreelectrically-conductive silver metal patterns comprises:

providing a substrate having a first supporting side and a secondopposing supporting side,

providing two or more thermally sensitive thin film patterns on two ormore respective portions on the first supporting side of the substrate,each of the two or more thermally sensitive thin film patternsconsisting essentially of:

(a) a silver complex comprising one or more reducible silver ionscomplexed with an α-oxy carboxylate and a 5- or 6-memberedN-heteroaromatic compound,

the silver complex being represented by the following formula (I):(Ag⁺)_(a)(L)_(b)(P)_(c)   (I)wherein L represents the α-oxy carboxylate; P represents the 5- or6-membered N-heteroaromatic compound; a is 1 or 2; b is 1 or 2; and c is1, 2, 3, or 4, provided that when a is 1, b is 1, and when a is 2, b is2;

(b) a hydroxy-free, nitrile-containing aprotic solvent having a boilingpoint at atmospheric pressure of at least 100° C. and less than 500° C.;and

(c) a polymer that is either (i) a hydroxy-containing cellulosic polymeror (ii) a non-cellulosic acrylic polymer having a halo- orhydroxy-containing side chain, which polymer is present in an amount ofat least 0.25 weight % and up to and including 15 weight %, based on thetotal weight of reducible silver ions in the silver complex;

thermally converting reducible silver ions in each of the two or morethermally sensitive thin film patterns on the first supporting side ofthe substrate to provide correspondingly two or moreelectrically-conductive silver metal-containing patterns on the firstsupporting side of the substrate, each electrically-conductive silvermetal-containing pattern consisting essentially of:

silver metal;

the α-oxy carboxylate;

the 5- or 6-membered N-heteroaromatic compound; and

either (i) the hydroxy-containing cellulosic polymer or (ii) thenon-cellulosic acrylic polymer having a halo- or hydroxy-containing sidechain; and

optionally, drying each of the two or more electrically-conductivesilver metal-containing patterns.

In some of these embodiments, the method can further comprise:

providing two or more opposing thermally sensitive thin film patterns ontwo or more respective portions on the second opposing supporting sideof the substrate, each of the two or more opposing thermally sensitivethin film patterns comprising:

a silver complex as defined by formula (I), a hydroxy-free,nitrile-containing aprotic solvent, and a (i) or (ii) polymer;

thermally converting reducible silver ions in each of the two or moreopposing thermally sensitive thin film patterns to provide two or moreopposing electrically-conductive silver metal-containing patterns on thesecond opposing supporting side of the substrate, each of the two ormore opposing electrically-conductive silver metal-containing patternsconsisting essentially of:

silver metal;

the α-oxy carboxylate;

the 5- or 6-membered N-heteroaromatic compound; and

either (i) the hydroxy-containing cellulosic polymer or (ii) thenon-cellulosic acrylic polymer having a halo- or hydroxy-containing sidechain; and

optionally, drying each of the two or more opposingelectrically-conductive silver metal-containing patterns.

In some of the methods noted above, each of the thermally sensitive thinfilm patterns on both the first supporting side and a second opposingsupporting side consists essentially of:

silver metal;

the same α-oxy carboxylate;

the same 5- or 6-membered N-heteroaromatic compound; and

the same (i) hydroxy-containing cellulosic polymer selected from thegroup consisting of hydroxypropylmethyl cellulose, hydroxypropylcellulose, hydroxyethyl cellulose, hydroxypropylmethyl cellulose, and amixture thereof, or the same (ii) non-cellulosic acrylic polymer that isderived from one or more (meth)acrylates, at least one of which(meth)acrylates having a halo- or hydroxy-containing side chain.

Moreover, the present invention provides an article comprising asubstrate having a first supporting side and a second opposingsupporting side, and further comprising on one or both of the firstsupporting side and the second opposing supporting side:

one or more electrically-conductive silver metal containing patterns,each consisting essentially of:

silver metal;

an α-oxy carboxylate;

a 5- or 6-membered N-heteroaromatic compound; and

a polymer that is either (i) a hydroxy-containing cellulosic polymer or(ii) a non-cellulosic acrylic polymer having a halo- orhydroxy-containing side chain.

The present invention is directed to: non-aqueous precursor compositionscontaining a silver complex comprising a silver ion complexed with oneor more α-oxy carboxylate compounds and one or more 5- or 6-memberedN-heteroaromatic compounds; uses of such compositions in methods toprovide electrically-conductive films or patterns; and methods forproducing and using same. For example, such silver complexes can beincorporated into silver “inks” or non-aqueous precursor compositionsthat comprise one or more hydroxy-free, nitrile-containing aproticsolvents, and one or more polymers that are either (i) ahydroxy-containing cellulosic polymer or (ii) a non-cellulosic acrylicpolymer having a halo- or hydroxy-containing side chain.

The silver complexes and non-aqueous precursor compositions containingsame can be used in various methods comprising the silver “ink” as auniform thermally sensitive thin film or as a thermally sensitive thinfilm pattern on a substrate, and heating the applied material atsuitable temperature and for a suitable time to generateelectrically-conductive silver metal (uniform layer or pattern) frommost or all the original reducible silver ions.

As the non-aqueous precursor compositions described herein are generallyin the form of clear liquids, it is possible to choose a wide array ofdeposition techniques when producing various articles and uses,including but not limited to flexographic printing, ink jet printing,screen printing, gravure printing, roll-to-roll coating, spraying, andother techniques that would be readily apparent to one skilled in theart.

The advantages described herein are achieved with the use of uniquesilver complexes with either the (i) or (ii) polymers described herein.Each complex comprises at least one reducible silver ion that iscomplexed with at least one α-oxy carboxylate, and at least one 5- or6-membered N-heteroaromatic compound.

Other advantages of the present invention would be readily apparent toone skilled in the art in view of the teaching provided herein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustration of the crystal structure of a silverion-containing complex as described in I-1 below.

FIG. 2 is an illustration of the crystal structure of a silverion-containing complex as described in I-2 below.

FIG. 3 is an illustration of the crystal structure of a silverion-containing complex as described in I-6 below.

FIG. 4 is a graphical representation of a typical cyclic voltammogram ofa silver ion-containing complex as described in I-11 below.

FIG. 5 is a graphical representation of a thermal gravimetric analysisas described below in Invention Example 1.

DETAILED DESCRIPTION OF THE INVENTION

The following discussion is directed to various embodiments of thepresent invention and while some embodiments can be desirable forspecific uses, the disclosed embodiments should not be interpreted orotherwise considered to limit the scope of the present invention, asclaimed below. In addition, one skilled in the art will understand thatthe following disclosure has broader application than is explicitlydescribed in the discussion of any embodiment.

Definitions

As used herein to define various components of the non-aqueous precursorcompositions, thermally sensitive thin films, thermally sensitive thinfilm patterns, or other materials used in the practice of the presentinvention, unless otherwise indicated, the singular forms “a,” “an,” and“the” are intended to include one or more of the components (that is,including plurality referents).

Each term that is not explicitly defined in the present application isto be understood to have a meaning that is commonly accepted by thoseskilled in the art. If the construction of a term would render itmeaningless or essentially meaningless in its context, the term shouldbe interpreted to have a standard dictionary meaning.

The use of numerical values in the various ranges specified herein,unless otherwise expressly indicated otherwise, are to be considered asapproximations as though the minimum and maximum values within thestated ranges were both preceded by the word “about.” In this manner,slight variations above and below the stated ranges may be useful toachieve substantially the same results as the values within the ranges.In addition, the disclosure of these ranges is intended as a continuousrange including every value between the minimum and maximum values aswell as the end points of the ranges.

Unless otherwise indicated, the term “weight %” refers to the amount ofa component or material based on the total amount of a non-aqueousprecursor composition, formulation, solution. In other embodiments,“weight %” can refer to the % solids (or dry weight) of a dry layer,coating, thin film, silver wire, or silver pattern.

Unless otherwise indicated herein, the terms “silver complex,” “silverion-containing complex,” and “complex” refer to materials used accordingto the present invention.

Unless otherwise indicated herein, the terms “non-aqueous precursorcomposition”, “thermally sensitive composition” and “thermally sensitivereducible silver ion-containing composition” refer to embodiments of thepresent invention.

Unless otherwise indicated herein, “thermal sensitivity” refers to theability for silver ions to be reduced to silver metal in a complex orthermally sensitive composition when heated at or above its glasstransition temperature.

Glass transition temperature, for example of the silver complexesdescribed herein can be measured using known principles and acommercially available instrument from, for example, TA Instruments,Perkin-Elmer, and Mettler Toledo.

Unless otherwise indicated, the term “non-aqueous” as applied to thenon-aqueous precursor composition or other solutions means that solventmedia used to form such compositions or solutions are predominantlyorganic in nature and water is not purposely added but may be present inan amount of less than 10 weight %, or particularly less than 5 weight%, or even less than 1 weight %, of the total weight of all solvents inthe solvent medium.

The average dry thickness of thermally sensitive thin films and silvermetal-containing thin films described herein can be the average of atleast 2 separate measurements taken, for example, using electronmicroscopy, optical microscopy, or profilometry.

Similarly, the average dry thickness or width of silver metal (includingsilver) lines, grid lines, or other silver metal-containing thin filmpattern features described herein can be the average of at least 2separate measurements taken, for example, using electron microscopy,optical microscopy, or profilometry.

The use of “dry” in reference to thickness and width refers toembodiments in which at least 50 weight % of originally presentsolvent(s) has been removed.

For clarification of definitions for any terms relating to polymers,reference should be made to “Glossary of Basic Terms in Polymer Science”as published by the International Union of Pure and Applied Chemistry(“IUPAC”), Pure Appl. Chem. 68, 2287-2311 (1996). However, anydefinitions explicitly set forth herein should be regarded ascontrolling.

As used herein, the term “polymer” is used to describe compounds withrelatively large molecular weights formed by linking together many smallreacted monomers. As the polymer chain grows, it folds back on itself ina random fashion to form coiled structures. With the choice of solvents,a polymer can become insoluble as the chain length grows and becomepolymeric particles dispersed in the solvent medium. These particledispersions can be very stable and useful in the non-aqueous precursorcompositions according to the present invention. In this invention,unless indicated otherwise, the term “polymer” refers to anon-crosslinked material. Thus, crosslinked polymeric particles differfrom the non-crosslinked polymeric particles in that the latter can bedissolved in certain organic solvents of good solvating property whereasthe crosslinked polymeric particles may swell but do not dissolve in theorganic solvent because the polymer chains are connected by strongcovalent bonds.

The term “copolymer” refers to polymers composed of two or moredifferent repeating or recurring units that are arranged along thecopolymer backbone.

The term “polymer backbone” refers to the chain of atoms in a polymer towhich a plurality of pendant groups can be attached. An example of sucha polymer backbone is an “all carbon” backbone obtained from thepolymerization of one or more ethylenically unsaturated polymerizablemonomers. Some polymer backbones can comprise both carbon andheteroatoms if the polymer is formed using condensation polymerizationreactions using suitable reactants.

Recurring units in polymeric binders described herein are generallyderived from the corresponding ethylenically unsaturated polymerizablemonomers used in a polymerization process, which ethylenicallyunsaturated polymerizable monomers can be obtained from variouscommercial sources or prepared using known chemical synthetic methods.

As used herein, the term “ethylenically unsaturated polymerizablemonomer” refers to a compound comprising one or more ethylenicallyunsaturated (—C═C—) bonds that are polymerizable using free radical oracid-catalyzed polymerization reactions and conditions. It is not meantto refer to chemical compounds that have only unsaturated —C═C— bondsthat are not polymerizable under these conditions.

Unless otherwise indicated, the term “group” particularly when used todefine a substituent or a moiety, can itself be substituted orunsubstituted (for example an “alkyl group” refers to a substituted orunsubstituted alkyl group) by replacement of one or more hydrogen atomswith suitable substituents (noted below) such as a fluorine atom.Generally, unless otherwise specifically stated, substituents on any“groups” referenced herein or where something is stated to be possiblysubstituted, include the possibility of any groups, whether substitutedor unsubstituted, which do not destroy properties necessary for expectedutility. It will also be understood for this disclosure and claims thatreference to a compound or complex of having a general structureincludes those compounds of other more specific formula that fall withinthe general structural definition. Examples of substituents on any ofthe mentioned groups can include known substituents such as: halogen(for example, chloro and fluoro); alkoxy, particularly those with 1 to 5carbon atoms (for example, methoxy and ethoxy); substituted orunsubstituted alkyl groups, particularly lower alkyl groups (forexample, methyl and trifluoromethyl), particularly either of thosehaving 1 to 6 carbon atoms (for example, methyl, ethyl, and t-butyl);and other substituents that would be readily apparent in the art.

Unless otherwise indicated, all voltages described herein are measuredversus SCE (saturated calomel electrode).

Uses

The deposition or patterning of functional electrodes, pixel pads, andconductive traces, lines, and tracks, which meet electricalconductivity, processing, and cost requirements for practicalapplications have been a great challenge. Silver metal is of interest inelectrically-conductive elements for electronic devices because silveris much lower in cost than gold and it possesses much betterenvironmental stability than copper.

The non-aqueous precursor compositions according to the presentinvention can be used for forming electrically-conductive metallicsilver patterns and electrodes for example in membrane touch switches(MTS), battery testers, biomedical, electroluminescent lamps, radiofrequency identification (RFID) antenna, flat panel displays such asplasma display panel (PDP) and organic light emitting diode (OLED)displays, printed transistors and thin film photovoltaics, and therebyreduce the numbers of steps for pattern formation in such devices.

The non-aqueous precursor compositions described herein can be used toprovide silver metal for various purposes, including but not limited to,the formation of electrically-conductive grids or patterns of fine wiresor other geometric forms, the formation of silver seed particles forelectroless plating with other electrically-conductive metals, and theformation of silver in various materials for antimicrobial activity.

More specifically, the silver complexes described herein areparticularly useful as part of non-aqueous precursor compositions thatcan be heated to provide silver metal in electrically-conductive metalthin films or metal patterns. These electrically-conductive metal thinfilms or patterns can be incorporated into various devices including butnot limited to, touch screens or other transparent display devices, andin modern electronics such as solar cell electrodes, electrodes inorganic thin film transistors (OTFTs), flexible displays, radiofrequency identification tags, light antennas, and other devices thatwould be readily apparent to one skilled in the art from the teachingherein.

The silver metal formed according to the present invention can also beused as catalytic sites for electrochemical plating using silver orother metals to improve electrically-conductivity of the resulting metalthin films or patterns.

Silver Complexes

The useful silver complexes are designed with only three essentialcomponents: (1) one or two reducible silver ions complexed with both (2)one or two α-oxy carboxylate molecules, and (3) one, two, three, or four5- or 6-membered N-heteroaromatic compound molecules, which componentsare described below.

In general, each useful silver complex can be represented by thefollowing formula (I):(Ag⁺)_(a)(L)_(b)(P)_(c)   (I)wherein L represents the α-oxy carboxylate; P represents the 5- or6-membered N-heteroaromatic compound; a is 1 or 2; b is 1 or 2; and c is1, 2, 3, or 4, provided that when a is 1, b is 1, and when a is 2, b is2.

In some embodiments:

(i) a and b are both 1 and c is 1 or 2;

(ii) a and b are both 2 and c is 2; or

(iii) a and b are both 2 and c is 4.

In addition, each silver complex according to the present invention hasat minimum solubility in a non-hydroxylic solvent (as defined below) orat least 5 g/liter at atmospheric pressure and ambient temperature (15°C. to 25° C.). It is particularly useful that this solubility feature ismeasured in acetonitrile that is one of the more useful hydroxy-free,nitrile-containing solvents.

Moreover, each silver complex of formula (I) can be defined usingoxidation potentials determined separately for the component parts, suchthat the “P” component that is a 5- or 6-membered N-heteroaromaticcompound having an oxidation potential of at least 1.0 V, at least 1.5V, or even at least 2.0 V vs. SCE; the “L” component, that is, the α-oxycarboxylate, has a first oxidation potential of at least 1.0 V vs. SCE;and upon decarboxylation of the α-oxy carboxylate, a second radical isgenerated that has an oxidation potential of less than 1.0 V vs. SCE.More specifically, the 5- or 6-membered N-heteroaromatic compound has anoxidation potential of greater than 1.5 V vs. SCE.

Further details of such properties are provided below.

It is very important that the silver complexes exhibit significantstability over time in that each silver complex meets a silver ionstability test such that when it is kept for 24 hours at ambienttemperature (15-25° C.) and under yellow safelight, less than 0.1 mol %of the original silver ion content in the silver complex is reduced tosilver metal (as tested by chemical analysis and UV-Vis absorptionspectroscopy).

Silver (Ag) Ions:

Each of the silver complexes comprises one or two reducible silver ions,that is, one or two Ag⁺ or Ag⁺¹ ions, as a first essential component.Each reducible silver ion is complexed with one or two α-oxy carboxylatecompounds. The complexation with an α-oxy carboxylate compound could bevia two oxygen atoms provided from the same molecule of an α-oxycarboxylate compound, or oxygen atoms provided from two molecules of thesame or different α-oxy carboxylate compounds.

Each silver complex of formula (I) shown above can be defined usingreduction potentials such that the Ag⁺¹ ion of the silver complex canhave a reduction potential of less than 1.0 V vs. SCE; or the Ag⁺¹ ionof the silver complex can have a reduction potential of less than 0.5 Vvs. SCE; or the Ag⁺¹ ion of the silver complex can have a reductionpotential of less than 0 V vs. SCE.

Silver ions can be provided using any suitable silver salt, and asdescribed below, they can be provided as part of a silver carboxylatesalt in which the carboxylate is an α-oxy carboxylate [L component informula (I)].

α-Oxy Carboxylates:

A second essential component of the silver complexes includes one ormore α-oxy carboxylate groups (moieties or components) in which theα-carbon atom attached directly to the carboxyl group [—C(═O)O—] has ahydroxy group, oxy, or an oxyalkyl substituent group. Thus, the α-oxycarboxylates can be either α-hydroxy carboxylates, α-alkoxycarboxylates, or α-oxy carboxylates. With the α-hydroxy carboxylates andα-alkoxy carboxylates, the remainder of the valences of that α-carbonatom can be filled with hydrogen or a branched or linear alkyl group(substituted or unsubstituted) as described below in more detail. Theα-oxy carboxylates can be supplied to prepare the silver complexes asthe corresponding free carboxylic acids or as corresponding alkali metalor ammonium salts.

In addition, the α-oxy carboxylate (L) generally has a molecular weightof 250 or less, or 150 or less, and it likely has a molecular weight ofat least 75 and up to and including 150.

It is important to note that the carboxylate groups in the silvercomplexes are not simple alkyl and aryl carboxylates that lack thehydroxyl, alkoxy, or oxy group at the α-position.

In formula (I) shown above, b is 1 or 2, and in the embodiments where bis 2, the two α-oxy carboxylate compounds within a single silver complexmolecule can be the same or different compounds. For example, the twoα-oxy carboxylate compounds can be provided as two of the same moleculesrepresented by either formula (II) or (III) as described below.Alternatively, the two α-oxy carboxylate compounds can be provided bytwo different molecules represented by formula (II), two differentmolecules represented by formula (III), or one molecule represented byformula (II) and one molecule represented by formula (III).

In some embodiments, L of formula (I) described above can be representedby the following formula (II):

wherein R₁, R₂, and R₃ are independently hydrogen or branched or linearalkyl groups. In most embodiments, at least one of R₁ through R₃ is abranched or linear alkyl group having from 1 to 8 carbon atoms, and anyof the hydrogen atoms in such branched or linear alkyl groups can bereplaced with a heteroatom such as a fluorine atom substituent.

In particularly useful embodiments of formula (II), R₁ is hydrogen or abranched or linear alkyl group having 1 to 3 carbon atoms (that is,substituted or unsubstituted methyl, ethyl, n-propyl, and iso-propyl),and R₂ and R₃ are independently branched or linear alkyl groups having 1to 8 carbon atoms (including iso- and tertiary alkyl groups having 3 to8 carbon atoms). In some embodiments, R₂ and R₃ are different branchedor linear alkyl groups as defined above. In addition, any of thehydrogen atoms in any of the R₁, R₂, and R₃ branched or linear alkylgroups optionally can be replaced with a fluorine atom; for example, theterminal carbon atom of a branched or linear alkyl group can have 1 to 3fluorine atoms.

Some particularly useful conjugate acids from which α-oxy carboxylates(L) of formula (II) can be selected from the group consisting of lacticacid, 2-hydroxybutyric acid, 2-hydroxy-3-methylbutyric acid,2-hydroxy-3,3-dimethylbutyric acid, 2-hydroxy-isobutyric acid,2-hydroxy-2-methylbutyric acid, 2-ethyl-2-hydroxybutyric acid,2-hydroxy-2,3-dimethylbutyric acid, 2-ethyl-2-methoxybutyric acid,2-methoxy-2-methylpropanoic acid, 1-hydroxycyclopentane-1-carboxylicacid, 2,3-dihydroxy-2,3-dimethylsuccinic acid, and2,4-dihydroxy-2,4-dimethylpentanedioic acid. As noted above, mixtures ofthese materials can be used in a specific silver complex if desired.

In other embodiments of the present invention, L is represented informula (I) by the following formula (III):

wherein R₄ is a branched or linear alkyl group having 1 to 8 carbonatoms, including branched iso- and tertiary alkyl groups having 3 to 8carbon atoms. In addition, any of the hydrogen atoms in any of thebranched or linear alkyl groups optionally can be replaced with afluorine atom; for example, the terminal carbon atom of an R₄ branchedor linear alkyl group can have 1 to 3 fluorine atoms.

Some useful conjugate acids from which the α-oxy carboxylate (L)represented by formula (III) can be selected from the group consistingof pyruvic acid, 3-methylpyruvic acid, 3,3-dimethylpyruvic acid,3,3-dimethyl-2-oxobutanoic acid, 3,3-dimethyl-2-oxopentanoic acid, and2,3-dioxosuccinic acid. Such materials can be readily obtained fromvarious commercial sources.

Some helpful understanding of the electrochemical behavior of the Lgroups in formula (I) is as follows in order to understand thisessential component of the silver complex.

Upon oxidation, the α-oxy carboxylate identified in formula (II)undergoes decarboxylation to produce a radical K. that can undergofurther oxidation as shown in the following Equation (1):

As noted herein, the silver complex can be characterized as having oneor more molecules of two components complexed with the silver ion:namely the α-oxy carboxylate compound and a nitrogen-containing Pcompound as defined below. The chemical structural features of all of P,R₁, R₂, and R₃ determine the oxidation potential of L (E_(ox1)) whereasR₁, R₂, and R₃ determine the oxidation potential of the radical K.(E_(ox2)).

An α-oxy carboxylate compound of the silver complex is capable oftransferring two electrons to the reducible silver ion. The firstelectron comes from oxidation of the α-oxy carboxylate to generate anα-oxy carboxyl radical L. that undergoes a bond cleavage reaction(decarboxylation) to give off CO₂ and to produce a second radical K.that can also desirably transfer a second electron to the reduciblesilver ion.

Thus, L can be a fragmentable α-oxy carboxylate wherein:

(1) L has a first oxidation potential of at least 1 V and up to andincluding 2 V (or for example, at least 1.2 V and up to and including 2V);

(2) the oxidized form of L undergoes a bond cleavage reaction to providethe second radical K. and CO₂; and

(3) the second radical K. has an oxidation potential ≤+1V (that is,equal to or more negative than +1V), and even less than or equal to0.5V.

α-Oxy carboxylates that satisfy criteria (1) and (2) above but notcriterion (3) are capable of donating one electron to the reduciblesilver ion and are referred to herein as “fragmentable one-electrondonors.” However, α-oxy carboxylates that meet all three criteria arecapable of donating two electrons and are referred to herein as“fragmentable two-electron donors,” and such components are particularlyuseful to provide a faster reduction of the silver ions.

Fragmentation of the oxidized form of L that is, α-oxy carboxyl radicalL., is an important feature in the silver metal-producing methodsaccording to the present invention. The kinetics of the fragmentationreaction can be measured by laser flash photolysis, a well-knowntechnique used to study properties of transient species as described forexample in “Absorption Spectroscopy of Transient Species,” W. G.Herkstroeter and I. R. Gould in Physical Methods of Chemistry Series(2nd. Ed.), Volume 8, 225-319, edited by B. Rossiter and R. Baetzold,John Wiley & Sons, New York, 1993. The rate constant of fragmentation ofthe α-oxy carboxylate radical is desirably faster than about 10⁹ persecond (that is, the lifetime of the α-oxy carboxylate radical should be10⁻⁹ seconds or less). The fragmentation rate constants can beconsiderably higher than this, namely in the 10² to 10¹³ s⁻¹ range. Inparticular, the fragmentation rate constant is desirably greater than10⁹ s⁻¹ and up to and including 10¹³ s⁻¹, or from 10¹⁰ s⁻¹ to andincluding 10¹³ s⁻¹. Fragmentation rate constants for some carboxylateradicals are known in the literature [for example see, T. MichaelBockman, Stephan M. Hubig, and Jay K. Kochi, J. Org. Chem. 1997, 62,2210-2221; James W. Hilborn and James A. Pincock, J. Am. Chem. Soc.1991, 113, 2683-2686; Daniel E. Falvey and Gary B. Schuster, J. Am.Chem. Soc. 1986, 108, 1420-1422]. Fragmentation rate constants for someα-hydroxy carboxyl radicals have also been measured using laser flashphotolysis and found to be very fast, that is 8×10¹¹ s⁻¹ (see, T.Michael Bockman, Stephan M. Hubig, and Jay K. Kochi, J. Org. Chem. 1997,62, 2210-2221). Since fragmentation rates of simple alkyl and arylcarboxyl radicals are usually small (about 10⁸ to 10⁹ s⁻¹), such simplealkyl and aryl carboxylates are not useful in the practice of thepresent invention.

The ability of the second radical K. described above to reduce silverion indicates that the oxidation potential of K. is nearly equal to ormore negative than the reduction potential of silver ion in the silvercomplex. In some useful embodiments, the second radical K., resultingfrom the decarboxylation reaction has an oxidation potential equal to ormore negative than −0.1 V or even more negative than −0.5 V. Forexample, this oxidation potential can be from −0.1 V to and including −2V, or even from −0.5 V to and including −2 V, or more likely from −0.1 Vto and including −1.0 V. In accordance with present invention, an α-oxycarboxylate ion that provides a second radical K. having an oxidationpotential more negative than −0.1 V is particularly advantageous. Alloxidation potentials are vs. SCE.

The oxidation potential of many such second radicals have been measuredby transient electrochemical and pulse radiolysis techniques as reportedby Wayner, D. D., McPhee, D. J., and Griller, D. in J Am. Chem. Soc.1988, 110, 132; Rao, P. S. and Hayon, E. in J. Am. Chem. Soc. 1974, 96,1287 and Rao, P. S, and Hayon, E. in J. Am. Chem. Soc. 1974, 96, 1295.The reported data demonstrate that the oxidation potentials of tertiaryradicals are less positive (that is, the tertiary radicals are strongerreducing agents) than those of the corresponding secondary radicals,which in turn are more negative than those of the corresponding primaryradicals.

5- or 6-Membered N-Heteroaromatic Compounds:

A third essential component of the silver complexes according to thepresent invention is the “P” compound of formula (I), which is a 5- or6-membered N-heteroaromatic compound. In many embodiments, P is a6-membered N-heteroaromatic compound.

Such 5- or 6-membered N-heteroaromatic compounds generally have anoxidation potential of at least 1.0 V vs. SCE, or greater than 1.5 V vs.SCE, or of at least 2.0 V vs. SCE.

It is also desirable that each 5- or 6-membered N-heteroaromaticcompound has a pK_(a) of at least 10 and up to and including 22, or moretypically of at least 10 and up to and including 15, as measured inacetonitrile. An experimental method for measuring pK_(a) and the pK_(a)values of some N-heteroaromatic bases are known (for example, seeKalijurand et al. J. Org. Chem. 2005, 70, 1019).

In general, the 5- or 6-membered N-heteroaromatic compounds are notpolymeric in nature and each has a molecular weight of 200 or less, orof 150 or less, or more likely of at least 80 and up to and including150.

By “5- or 6-membered,” it is meant that the N-heteroaromatic compoundhas either 5 or 6 atoms in the heterocyclic aromatic ring, at least oneof which atoms is a nitrogen atom. A worker of ordinary skill in the artof chemistry would be able to design any of the heteroaromatic ringsthat are possible using the laws of chemistry. In general, suchheterocyclic aromatic rings generally have at least one carbon atom andat least one nitrogen atom in the ring.

In formula (I) shown above, c is 1, 2, 3, or 4, and in the embodimentswhere c is 2, 3, or 4, the multiple 5- or 6-membered N-heteroaromaticcompound molecules within the single silver complex molecule can be thesame or different. For example, in such embodiments, one or more of the5- or 6-membered N-heteroaromatic compounds can be pyridine and other 5-or 6-membered N-heteroaromatic compound(s) can be 2-methylpyridine.

Moreover, it is desirable that the 5- or 6-membered N-heteroaromaticcompound is selected from the group consisting of pyridine,2-methylpyridine, 4-methylpyridine, 2,6-dimethylpyridine,2,3-dimethylpyridine, 3,4-dimethylpyridine, 4-pyridylacetone,3-chloropyridine, 3-fluoropyridine, oxazole, 4-methyloxazole, isoxazole,3-methylisoxazole, pyrimidine, pyrazine, pyridazine, and thiazole. Otheruseful 5- or 6-membered N-heteroaromatic compounds would be readilyapparent to one skilled in the art from the foregoing description.

Representative 5- or 6-membered N-heteroaromatic compounds can bereadily obtained from various commercial chemical suppliers located invarious countries.

Method of Making Complexes:

In general, the silver complexes can be prepared by making a slurry ofone or more silver α-oxy carboxylates in suitable solvent mediumcomprising one or more hydroxy-free, nitrile-containing aprotic solvents(described below) at a general concentration of at least 0.1 mol/l andto and including 30 mol/l; and at room temperature, adding either one ormore 5- or 6-membered N-heteroaromatic compounds gradually to obtain aclear solution in the resulting reaction solution. Specific details forthese synthetic methods are provided below with the working Examplesbelow.

Once prepared, the silver complexes can be stored in the form of solid(after the solvent medium is removed by evaporative methods), or left inthe reaction solution under conditions that are optimum for long-termstability (that is, negligible premature reduction of silver ion tosilver metal).

Some particularly useful silver complexes prepared the present inventionare represented by formula (I):(Ag⁺)_(a)(L)_(b)(P)_(c)   (I)wherein:

a, b, and c are as defined above;

L has a molecular weight of 250 or less, and is represented by either ofthe following formula (II) or (III):

wherein R₁ is hydrogen or an alkyl group having 1 or 2 carbon atoms; R₂and R₃ are independently branched or linear alkyl groups having 1 to 8carbon atoms, wherein any of the hydrogen atoms in the R₁, R₂, and R₃branched or linear alkyl groups can optionally be replaced with afluorine atom; and R₄ is a branched or linear alkyl group having 1 to 8carbon atoms, wherein any of the hydrogen atoms optionally are replacedwith fluoride atoms; and

P is a 5- or 6-membered N-heteroaromatic compound that is selected fromthe group consisting of pyridine, 2-methylpyridine, 4-methylpyridine,2,6-dimethylpyridine, 2,3-dimethylpyridine, 3,4-dimethylpyridine,4-pyridylacetone, 3-chloropyridine, 3-fluoropyridine, oxazole,4-methyloxazole, isoxazole, 3-methylisoxazole, pyrimidine, pyrazine,pyridazine, and thiazole.

Non-Aqueous Precursor Compositions

The non-aqueous precursor compositions contain only three essentialcomponents for the purpose of providing silver metal during a thermalsilver reduction process: (a) one or more silver complexes as describedabove; (b) a solvent medium comprising one or more hydroxy-free,nitrile-containing aprotic solvents as described below; and (c) one ormore (i) or (ii) polymers as described below. Photosensitizers are notneeded in the practice of the present invention. No other components arepurposely added to the non-aqueous precursor compositions so that theyare simple solutions that exhibit rapid silver metal formation forvarious methods and results. The incorporation of materials other thanthe three components (a), (b), and (c) is likely to impede thegeneration of metallic silver.

The (a), (b), and (c) components can be put together in general bymixing them under “safe light” (yellow light) conditions at roomtemperature. This mixing can occur in suitable solvent medium (asdescribed below) comprising one of more of the (b) solvents. Theresulting non-aqueous precursor composition can be provided in liquidform having a viscosity of at least 1 centipoise and up to and including1,000 centipoises at 25° C.

The one or more silver complexes can be present in an amount to providereducible silver ions in an amount of at least 30 weight % and up to andincluding 90 weight %, or more likely reducible ions in an amount of atleast 40 weight % and up to and including 75 weight %, based on thetotal weight of the non-aqueous precursor composition.

In some embodiments, the non-aqueous precursor composition can comprisetwo or more different silver complexes as defined by Structure (I)above.

The non-aqueous precursor composition can exhibit long term stability asdemonstrated by a reducible silver ion stability test such that when thenon-aqueous precursor composition is held at ambient temperature (20° C.to 25° C.) and under yellow safelight for 24 hours, less than 0.1 mol %of its original silver ion content is reduced to silver metal. Theextent of silver reduction can be confirmed by the presence or absenceof silver plasmon band (at about 400 nm) by UV-vis absorptionspectroscopy. The appearance and strength of this silver plasmon bandindicates the formation and concentration of silver nanoparticles.

Solvent Medium:

The essential silver complex is generally solubilized in a suitablesolvent medium that consists essentially of one or more hydroxy-free,nitrile-containing aprotic solvents that include but are not limited to,acetonitrile, benzonitrile, butyronitrile, propionitrile,isovaleronitrile, valeronitrile, and a mixture of two or more of suchorganic solvents. It is also desirable that such organic solvents do notparticipate in any redox reaction. That is, such organic solvents shouldnot be capable under general preparation, storage, and use conditions toreduce silver ion by transferring electrons or to oxidize an α-oxycarboxylate to accept electrons. Such reactions would negatively impactthe thermal stability of the non-aqueous precursor compositions.

Water is not purposely added to the solvent medium, and if water ispresent, it should be present at no more than 5 weight % based on thetotal weight of the solvent medium.

(i) and (ii) Polymers:

A third essential component is one or more polymers that fall intoeither of two classes of polymers defined below. It is also possiblethat mixtures of polymers from each class, or mixtures of polymers fromboth classes, can be used. When used in mixtures, the two or moredifferent (i) or (ii) [or both (i) and (ii)] classes of polymers can bepresent in the same or different amounts within the total amountpolymers in the non-aqueous precursor composition

The useful (i) polymers are hydroxy-containing cellulosic polymers. Bothhydroxy-containing cellulose esters and hydroxy-containing celluloseethers can be used in the present invention. Representative usefulpolymers for the practice of the present invention include but are notlimited to, hydroxypropyl methylcellulose, hydroxypropyl cellulosephthalate, hydroxypropyl cellulose, hydroxyethyl cellulose, andcombinations thereof. Hydroxypropyl methylcellulose, hydroxypropylcellulose, and hydroxyethyl cellulose, individually or in mixtures, areparticularly useful.

Each of the useful (i) hydroxy-containing cellulosic polymers can bereadily obtained from various commercial sources in the world, or theycan be prepared using known starting materials, reaction conditions, andknown synthetic procedures.

Useful (ii) polymers are generally non-cellulosic acrylic polymersderived from one or more ethylenically unsaturated polymerizablemonomers that are substituted or unsubstituted acrylates or substitutedor unsubstituted methacrylates, collectively identified herein as“(meth)acrylates.” It is also essential that such (meth)acrylatescomprise one or more halo-containing or hydroxy-containing side chains.In other words, the ethylenically unsaturated polymerizable monomersfrom which the (ii) polymers can be derived generally comprise at leastone pendant group attached to the polymerizable vinylic group thatcontains a hydroxy group or a halo group (such as a fluoro, chloro, orbromo group). Both hydroxy groups and halo groups can be present in thesame ethylenically unsaturated polymerizable monomer if desired.

A variety of ethylenically unsaturated polymerizable monomers can beused to provide the (ii) polymers as homopolymers or copolymers.Representative monomers having either a hydroxy-group or a halo-group ina pendant moiety include but are not limited to, vinyl acetate, vinylbutyrate, vinyl propionate, hydroxyethyl acrylate, hydroxyethylmethacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate,chloroethyl acrylate, chloroethyl methacrylate, 1-chloropropyl acrylate,and others that would be readily apparent to one skilled in the art.Such monomers can also be co-polymerized with other ethylenicallyunsaturated polymerizable (meth)acrylates that do not contain a halo orhydroxy group, such as for example, methyl methacrylate, methylacrylate, ethyl methacrylate, n-propyl methacrylate, n-butylmethacrylate, and others that would be readily apparent to one skilledin the art.

In the resulting (ii) polymer, the recurring units comprising thehalo-containing side chain, hydroxy-containing side chain, or both typesof side chains, can comprise at least 25 mol %, or even at least 60 mol%, and up to and including 100 mol % of the total recurring units.

Some of the (ii) polymers can be readily purchased from variouscommercial sources, or they can be readily prepared using readilyavailable or prepared starting monomers, initiators, and solvents usingknown polymerization and isolation techniques.

The one or more (i) or (ii) polymers described herein can be present inthe non-aqueous precursor composition in a total amount of at least 0.25weight % and up to and including 15 weight %, or more likely of at least2 weight % and up to and including 15 weight %, or even at least 2weight % and up to and including 12 weight %, based on the total weightof reducible silver ions in the silver complex.

Precursor Articles

The silver complexes and non-aqueous precursor compositions describedherein can be used to provide “precursor” articles that can then be usedin various operations to provide electrically-conductive silvermetal-containing thin film layers or electrically-conductive silvermetal-containing thin film patterns for various uses in “productarticles” as described below.

The term “precursor article” refers to an article (or element) designedto have a substrate having thereon a thermally sensitive thin film orthermally sensitive thin film pattern comprising a non-aqueous precursorcomposition as noted above and thus, is thus an article in which silverreduction has not occurred to any appreciable extent.

The term “product article” then refers to an article (or element) inwhich silver ion reduction has occurred to at least some extent andhopefully to a significant extent (for example, at least 80 mol % oreven at least 95 mol % conversion of the original reducible silver ionsin the precursor article) during chosen operations as described below.Such product articles comprise a substrate having thereon a silvermetal-containing thin film or silver metal-containing thin film patternconsisting essentially of silver metal, residual α-oxy carboxylate,residual 5- or 6-membered N-heteroaromatic compound, and residual one ormore (i) or (ii) polymers.

Both precursor articles and product articles have at least one featurein common, that is a suitable substrate that generally has two planarsurfaces: a first supporting side (or surface) and a second opposingsupporting side (or surface). Such substrates can have any suitable formsuch as sheets of any desirable size and shape, elongated fibers orwoven fibers (such as in textiles) or other porous materials, polymericbeads of regular or irregular surface configuration (such as a curved ornon-planar surface), and especially continuous webs of various materialsthat can be supplied, used, or stored as rolls.

More specifically, a uniform thermally sensitive thin film or one ormore thermally sensitive thin film patterns are provided in a suitablemanner on one or more supporting (planar) sides of a suitable substrateto provide a precursor article. Typically, thermally sensitive thinfilms or thermally sensitive thin film patterns are initially “wet”during and immediately after application to the substrate but thesolvent medium can be removed as described below to provide the desiredthermally sensitive thin films or thermally sensitive thin filmpattern(s).

The non-aqueous precursor compositions can be applied in a uniform orpattern-wise manner to any suitable substrate using any means forapplication, such as dip coating, roll coating, hopper coating, screenprinting, spray coating, spin coating, inkjet printing,photolithographic imprinting, flexographic printing using printingelements including flexographic printing members (such as flexographicprinting plates and flexographic printing sleeves), lithographicprinting using lithographic printing plates, and gravure or intaglioprinting using appropriate printing members. Inkjet printing andflexographic printing are particularly useful for providing thermallysensitive thin film patterns on one or both supporting sides of thesubstrate.

Suitable substrates (also known as “receiver elements”) can be composedof any suitable material that does not inhibit the purpose of thepresent invention to form electrically-conductive silver metal within auniform thin film or thin film pattern. For example, substrates can beformed from materials including but are not limited to, polymeric films,metals, glasses (untreated or treated for example with tetrafluorocarbonplasma, hydrophobic fluorine, or a siloxane water-repellant material),silicon or ceramic materials such as ceramic wafers, fabrics, papers,and combinations thereof (such as laminates of various films, orlaminates of papers and films) provided that a uniform thin film or thinfilm pattern can be formed thereon in a suitable manner and followed byirradiation on at least one supporting side thereof. The substrate canbe transparent or opaque, and rigid or flexible. The substrate caninclude one or more auxiliary polymeric or non-polymeric layers or oneor more patterns of other materials before the non-aqueous precursorcomposition is applied.

Suitable substrate materials for forming precursor and product articlesprepared according to the present invention include but are not limitedto, metallic films or foils, metallic films on polymer, glass, orceramic materials, metallic films on electrically conductive filmsupports, semi-conducting organic or inorganic films, organic orinorganic dielectric films, or laminates of two or more layers of suchmaterials. For example, useful substrates can include polymeric filmssuch as poly(ethylene terephthalate) films, poly(ethylene naphthalate)films, polyimide films, polycarbonate films, polyacrylate films,polystyrene films, polyolefin films, and polyamide films, silicon andother ceramic materials, metal foils such as aluminum foils, cellulosicpapers or resin-coated or glass-coated papers, glass or glass-containingcomposites, metals such as aluminum, tin, and copper, and metalizedfilms. Porous fabrics, glasses, and polymeric webs can also be used.

Particularly useful substrates are glasses and ceramics, and continuousflexible webs of polyesters films.

Either or both supporting sides (or surfaces) of the substrate can betreated for example with a primer layer or electrical or mechanicaltreatments (such as graining) to render that surface “receptive” toimprove adhesion of the non-aqueous precursor composition and resultingsilver-containing thin film or silver-containing thin film pattern. Anadhesive layer can be disposed on the substrate and this adhesive layercan have various properties in response to stimuli (for example, it canbe thermally activated, solvent activated, or chemically activated) andthat serves to provide a receptive layer. Useful adhesive materials ofthis type are described for example in [0057] of U.S. Patent Application2008/0233280 (Blanchet et al.).

In some embodiments, the substrate comprises a separate receptive layeras a receptive surface disposed on the supporting side of the substrate,which receptive layer and substrate can be composed of a material suchas a suitable polymeric material that is highly receptive of thenon-aqueous precursor composition. Such a receptive layer can have anysuitable dry thickness of at least 0.05 μm when measured at 25° C.

The two (planar) supporting sides of the substrate, especially polymericsubstrates, can be treated by exposure to corona discharge, mechanicalabrasion, flame treatments, or oxygen plasmas, or by coating withvarious polymeric films, such as poly(vinylidene chloride) or anaromatic polysiloxane as described for example in U.S. Pat. No.5,492,730 (Balaba et al.) and U.S. Pat. No. 5,527,562 (Balaba et al.)and U.S. Patent Application Publication 2009/0076217 (Gommans et al.).

Useful substrates can have a desired dry thickness depending upon theeventual use of the product article formed therefrom, for example, itsincorporation into various products articles or optical or displaydevices. For example, the substrate dry thickness (including alltreatments and auxiliary layers) can be at least 0.001 mm and up to andincluding 10 mm, and especially for polymeric films, the substrate drythickness can be at least 0.008 mm and up to and including 0.2 mm.

The substrate used to prepare the precursor and product articlesdescribed herein can be provided in various forms, such as for example,individual sheets in any size or shape, and continuous webs such ascontinuous webs of transparent substrates including transparentpolyester substrates that are suitable for roll-to-roll operations. Suchcontinuous webs can be divided or formed into individual first, second,and additional portions on first and second opposing supporting sidesthat can be used to form the same or different thermally sensitive thinfilm patterns in different portions of a supporting side (such as thefirst supporting sides) as well as same or different thermally reduced,electrically-conductive silver-containing thin film patterns from thesame or different non-aqueous precursor compositions.

In general, in the precursor article, the one or more silver complexescan be present in the thermally sensitive thin film or the one or morethermally sensitive thin film patterns in a total amount of at least 95weight % and up to and including 99.5 weight % based on the total dryweight of the thermally sensitive thin film or the one or more thermallysensitive thin film patterns.

In some embodiments, a precursor article can further comprise one ormore dry thermally sensitive thin film patterns on the second opposingsupporting side of the substrate, each of the one or more dry thermallysensitive thin film patterns disposed on the second opposing supportingside, comprising:

a) one or more silver complexes as described above; and

c) one or more (i) or (ii) polymers as described above.

Product Articles

The product articles provided by the methods according to the presentinvention described below generally have the same structure andcomponents as the precursor articles except that most or all of thereducible silver ions have been reduced to electrically-conductivesilver metal in the corresponding electrically-conductive thin films orelectrically-conductive thin film patterns. The product articles can beprovided in any suitable form such as individual sheets of any suitablesize and shape, films or webs whose ends are attached to each other,wound rolls of continuous material with or without a core material,spindle, or mandrel.

In other embodiments, where silver complexes, non-aqueous precursorcompositions, and methods can be used to generateelectrically-conductive metallic silver patterns and electrodes withinvarious devices, including but not limited to, membrane touch switch(MTS), battery testers, biomedical, electroluminescent lamps, radiofrequency identification (RFID) antenna, electromagnetic shields, flatpanel displays such as plasma display panel (PDP) and organic lightemitting diode (OLED) display, printed transistors and circuits, thinfilm photovoltaics, and other devices that would be readily apparent toone skilled in the art. In other words, such “product” articles aredevices themselves rather than articles that are incorporated into adevice. Alternatively, the product articles are devices themselves thatalso have another product article incorporated therein.

Electrically-conductive thin film patterns can be created usingphotolithography to create high-fidelity features, Both positive andnegative patterning processes may be used to create such patterns.

Such product articles comprise a substrate having a first supportingside and a second opposing supporting side. On at least the firstsupporting side, are:

an electrically-conductive silver metal-containing thin film or one ormore electrically-conductive silver metal-containing thin film patterns,consisting essentially of:

silver metal;

residual α-oxy carboxylate (residual amounts of the L component fromformula (1)) as described above;

residual 5- or 6-membered N-heteroaromatic compound (residual amounts ofthe P component from formula (1)); and

residual (i) or (ii) polymer as described herein.

Depending upon how the precursor article is designed, the productarticle can comprise two or more electrically-conductive silvermetal-containing thin film patterns in different portions on the firstsupporting side of the substrate.

In addition, a product article can further comprise one or moreelectrically-conductive silver metal-containing thin film patterns indifferent portions on the second opposing supporting side of thesubstrate,

each of these one or more electrically-conductive silvermetal-containing thin film patterns consisting essentially of:

silver metal;

residual α-oxy carboxylate (that is, residual amounts of the L componentof formula (1) as described above);

residual 5- or 6-membered N-heteroaromatic compound (that is, residualamounts of the P component of formula (1) described above); and

residual (i) or (ii) polymer as described herein.

For example, in such embodiments, the product articles can consistessentially of:

silver metal;

residual α-oxy carboxylate having a molecular weight of 150 or less, andthat is represented by either the following formula (II) or (III):

wherein R₁ is hydrogen or a branched or linear alkyl group having 1 to 3carbon atoms, R₂ and R₃ are independently branched or linear alkylgroups having 1 to 8 carbon atoms, wherein any of the hydrogen atoms inthe R₁, R₂, and R₃ branched or linear alkyl groups optionally can bereplaced with a fluorine atom, and R₄ is a branched or linear alkylgroup having 1 to 8 carbon atoms wherein any of the hydrogen atomsoptionally can be replaced with a fluorine atom;

residual 5- or 6-membered N-heteroaromatic compound that is selectedfrom the group consisting of pyridine, 2-methylpyridine,2,6-dimethylpyridine, 3-chloropyridine, 3-fluoropyridine, oxazole,4-methyloxazole, isoxazole, 3-methylisoxazole, pyrimidine, pyrazine,pyridazine, and thiazole; and

residual hydroxypropyl cellulose, hydroxyethyl cellulose, hydroxypropylmethylcellulose, or mixtures thereof, or residual polymers derived fromone or more (meth)acrylates, at least one of which (meth)acrylateshaving a halo- or hydroxy-containing side chain.

Method for Providing Silver Metal

The precursor articles are prepared and used by firstly providing asuitable thermally sensitive thin film (or thermally sensitive thin filmpattern) on a substrate as described above. This can be accomplished inseveral ways.

In some embodiments, a non-aqueous precursor composition according tothe present invention can be disposed in a uniform manner onto one orboth supporting sides of the substrate (with or without adhesiontreatments), such as a polymeric film (for example, as a continuouspolyester web), glass, paper, cardboard, or ceramic material Suchcomposition application can be carried out for example, uniform inkjetprinting or using a blade coating, gap coating, slot die coating, spincoating, X-slide hopper coating, or knife on roll operation.

The one or more silver complexes can be present in the dry thermallysensitive thin film or thermally sensitive thin film pattern in anamount of at least 95 weight % and up to and including 99.5 weight %based on the total dry weight of the thermally sensitive thin film orthermally sensitive thin film pattern.

The resulting thermally sensitive thin films generally have a dryaverage thickness of at least 100 nm and up to and including 1,500 nm,or more likely at least 500 nm and up to and including 1000 nm(“average” determined by two or more measurements in differentlocations). The dry thickness can vary to some degree throughout thethermally sensitive thin film. The term “uniform” in this context doesnot necessary mean that the dry thickness must always be the same, butthat the entire surface of the supporting side of the substrate iscompletely covered.

Alternative to depositing the non-aqueous precursor composition in auniform manner, it can be applied to the substrate (one or bothsupporting sides) in a patternwise fashion using patterning techniquesdescribed below such as flexographic printing or inkjet printing toprovide one or more thermally sensitive thin film patterns.

Any applied thermally sensitive thin film pattern can comprise a grid oflines (or other shapes including circles or an irregular network), eachhaving a dry average thickness (or width) of at least 1000 nm and up toand including 10 mm, or typically of at least 5 μm and up to andincluding 1 mm, and the optimal dry thickness (or width) can be tailoredfor an intended use.

In some embodiments, the same or different non-aqueous precursorcomposition can be applied in a suitable manner in different portions onboth the first supporting side and the second opposing supporting sideof the substrate to form “duplex” or dual-sided precursor articles, andeach applied non-aqueous precursor composition can be in the form of thesame or different thermally sensitive thin film pattern.

In many embodiments, a non-aqueous precursor composition is applied onone or both supporting sides of the substrate (for example as aroll-to-roll web) using a relief element such as elastomeric reliefelements derived from flexographic printing plate precursors, many ofwhich are known in the art and some are commercially available, forexample as the CYREL® Flexographic Photopolymer Plates from DuPont andthe Flexcel SR and NX Flexographic plates from Eastman Kodak Company.

Particularly useful elastomeric relief elements are derived fromflexographic printing plate precursors and flexographic printing sleeveprecursors, each of which can be appropriately imaged (and processed ifneeded) to provide the relief elements for “printing” suitable thermallysensitive thin film patterns as described for example, in U.S. Pat. No.7,799,504 (Zwadlo et al.) and U.S. Pat. No. 8,142,987 (Ali et al.) andU.S. Patent Application Publication 2012/0237871 (Zwadlo), thedisclosures of all of which are incorporated herein by reference fordetails of such flexographic printing member precursors.

In other embodiments, the elastomeric relief element is provided from adirect (or ablation) laser-engravable elastomer relief elementprecursor, with or without integral masks, as described for example inU.S. Pat. No. 5,719,009 (Fan), U.S. Pat. No. 5,798,202 (Cushner et al.),U.S. Pat. No. 5,804,353 (Cushner et al.), U.S. Pat. No. 6,090,529(Gelbart), U.S. Pat. No. 6,159,659 (Gelbart), U.S. Pat. No. 6,511,784(Hiller et al.), U.S. Pat. No. 7,811,744 (Figov), U.S. Pat. No.7,947,426 (Figov et al.), U.S. Pat. No. 8,114,572 (Landry-Coltrain etal.), U.S. Pat. No. 8,153,347 (Veres et al.), U.S. Pat. No. 8,187,793(Regan et al.), and U.S. Patent Application Publications 2002/0136969(Hiller et al.), 2003/0129530 (Leinenback et al.), 2003/0136285 (Telseret al.), 2003/0180636 (Kanga et al.), and 2012/0240802 (Landry-Coltrainet al.), the disclosures of all of which are incorporated herein.

When the noted elastomeric relief elements are used in the presentinvention, the thermally sensitive reducible silver ion-containingcomposition can be applied in a suitable manner to the uppermost reliefsurface (raised surface) in the elastomeric relief element. Applicationto a substrate can be accomplished in a suitable procedure and it isdesirable that as little as possible is coated onto the sides (slopes)or recesses of the relief depressions. Anilox roller systems or otherroller application systems, especially low volume Anilox rollers, below2.5 billion cubic micrometers per square inch (6.35 billion cubicmicrometers per square centimeter) and associated skive knives can beused.

In such embodiments, the non-aqueous precursor composition can have aviscosity during this application of at least 1 cps (centipoise) and upto and including 5000 cps, or at least 1 cps to and up to and including1500 cps. The non-aqueous precursor composition can be fed from anAnilox or other roller inking system in a measured amount for eachprinted precursor article.

Once the thermally sensitive thin films or thermally sensitive thin filmpatterns are provided, such precursor articles can be then appropriatelyheated at a temperature that is at or below the glass transitiontemperature of the silver complex for a time sufficient to convert atleast 90 mol % (or even at least 95 mol %) of the original reduciblesilver metal ions to silver metal. It is desirable to carry out thisheating in ambient atmosphere (for example, in air) to provide productarticles comprising silver metal-containing thin films or one or moresilver metal-containing thin film patterns. Such heating can be carriedout in a desired temperature directly, or it can be carried out in astep-wise manner wherein the temperature is slowly ramped up from roomtemperature over a desired time to the desired final temperature. Withroutine experimentation, a skilled worker can determine the optimal timeand temperature for the desired thermal reduction of the reduciblesilver ions.

Each precursor article can be heated individually as a single element,or in alternative embodiments, as a web (for example, a roll-to-rollcontinuous web) containing multiple precursor articles in multipleportions of the continuous web that is passed through exposure stations,or the heating device is passed over the continuous web. The same ordifferent non-aqueous precursor compositions can be applied (forexample, printed) on both supporting sides of the substrate whether itis in the form of a single element or continuous web. In manyembodiments, different thermally sensitive thin film patterns can beformed on opposing supporting sides of the substrate (or continuousweb).

The result of such thermal exposure of a precursor article is a productarticle as described above comprising the substrate (for example,individual sheets or a continuous web) and having thereon either anelectrically-conductive silver metal-containing thin film or one or moreelectrically-conductive silver metal-containing thin film patterns onone or both supporting sides of the substrate.

In general, the electrically-conductive silver metal-containing thinfilm or electrically-conductive silver-containing thin film patterns hasa resistivity of less than 10⁶ ohms/□ as measured using a 4-point probedevice. Each electrically-conductive silver-containing thin film orelectrically-conductive silver-containing thin film pattern can have aresistivity of less than 1000 ohms/□, or a resistivity of less than 500ohm/□, or even less than 10 ohms/□.

After thermal exposure, the product articles can be contacted (washed)with water for up to 5 minutes at a temperature of at least 20° C. andup to and including 90° C. Such water contacting can be used to removeimpurities as well as to enhance electrical conductivity of theelectrically-conductive silver metal-containing thin film or one or moreelectrically-conductive silver metal-containing thin film patterns.Residual water can be removed after this step using any suitable dryingoperation, for example as described above for other drying operations.

When such a method is carried out, all thermally sensitive thin filmpatterns on both the first supporting side and the second opposingsupporting side of the continuous substrate can be provided using thesame or different flexographic printing members.

The following Examples are provided to illustrate the practice of thisinvention and are not meant to be limiting in any manner.

Most reagents and solvents used in the following Examples can beobtained from various commercial sources such as VWR, Sigma-AldrichChemical Co. (Milwaukee, Wis., USA) and Fisher Scientific (Pittsburgh,Pa., USA).

C-1: Preparation of Silver Isobutyrate Pyridine Complex

To a slurry of silver isobutyrate (1 g, 5.18 mmol) in acetonitrile (4ml), pyridine (0.41 g, 5.18 mmol) was added and the resulting reactionmixture was stirred at 25° C. until a clear solution was obtained. Theclear reaction solution was then stirred for 10 minutes and acetonitrilewas slowly removed at room temperature to obtain a white solid of thedesired silver isobutyrate pyridine complex that was characterized by ¹HNMR (CD₃CN).

Attempted Thermal Generation of Electrically-Conductive Silver MetalUsing Silver Isobutyrate Pyridine Complex:

The silver isobutyrate pyridine complex noted above (0.4 g) wasdissolved in acetonitrile (1 ml). The resulting photosensitive silverion-containing composition was spin coated onto a glass plate substrateat 800 rpm and the resulting precursor article with thin film on theglass substrate was heated on a hot plate at 150° C. for 10 minutes. Thesheet resistivity of the resulting printed metallic silver features wasmeasured using a 4-point probe device and found to be non-electricallyconductive. The thin film resistivity did not change after washing itwith a brine (sodium chloride) solution (0.1 molar) for 10 seconds.

This example demonstrates that upon heating, the silver ion-containingcomposition comprising a complex formed from reducible silver ions, analkyl carboxylate, and a 5- or 6-membered N-heteroaromatic compoundgenerates a film of electrically-conductive silver metal.

I-1: Preparation of Silver Lactate 2,6-Dimethylpyridine Complex

To a slurry of silver lactate (1.0 g, 5.076 mmol) in acetonitrile (4ml), 2,6-dimethylpyridine (0.54 g, 5.08 mmol) was added and the reactionmixture was stirred to obtain a clear reaction solution. The resultingreaction solution was stirred at 25° C. for 10 minutes and acetonitrilewas slowly removed at room temperature to obtain a white solid of thedesired silver lactate 2,6-dimethylpyridine complex having the crystalstructure as shown in FIG. 1 and confirmed by NMR (CD₃CN).

I-2: Preparation of Silver Lactate 2,4,6-Trimethylpyridine Complex

To a slurry of silver lactate (1.0 g, 5.08 mmol) in acetonitrile (5 ml),2,4,6-trimethylpyridine (0.609 g, 5.08 mmol) was added and the resultingreaction solution was stirred at 25° C. for 10 minutes. The acetonitrilewas slowly removed at room temperature to obtain a white solid of thedesired silver lactate 2,4,6-dimethylpyridine complex having the crystalstructure as shown in FIG. 2 and confirmed by ¹H NMR (CD₃CN).

I-3: Preparation of Silver Lactate 3-Chloropyridine Complex

To a slurry of silver lactate (1.0 g, 5.08 mmol) in acetonitrile (5 ml),3-chloropyridine (1.72 g, 15.24 mmol) was added and the resultingreaction solution was stirred at 25° C. for 10 minutes. The acetonitrilewas slowly removed at room temperature to obtain a white solid of thedesired silver lactate 3-chloropyridine complex as confirmed by ¹H NMR(CD₃CN).

I-4: Preparation of Silver 2-Hydroxyisobutyrate Pyridine Complex

Silver 2-hydroxyisobutyrate was prepared as follows. A solution of 50%sodium hydroxide solution (58.8 g; 0.735 moles) was added to 1.05 literof chilled (15° C.) deionized (DI) water employing mechanical stirringand external cooling at 15° C. 2-Hydroxyisobutyric acid (78.1 g; 0.750moles) was added in portions, maintaining the resulting reactionsolution temperature near or below ambient temperature. After thisaddition, the homogeneous reaction solution was stirred at 15° C. for 30minutes to ensure complete reaction. Silver nitrate (127.4 g; 0.75 mole)in deionized water (187.5 ml) was slowly added to the sodium2-hydroxyisobutyrate solution over 10 minutes. During the addition, aprecipitate formed. The reaction solution was stirred at 15° C. for 30minutes, and the slurry was filtered (medium frit size 90) and washedwith water (50 ml). The collected solid was further washed with two 200ml portions of acetone and air dried to provide the desired product ofsilver 2-hydroxyisobutyrate at 60% yield.

To a slurry of the formed silver 2-hydroxyisobutyrate (1 g, 4.76 mmol)in acetonitrile (5 ml), pyridine (0.75 g, 9.52 mmol) was added to obtaina clear reaction solution that was stirred for an additional 10-15minutes at 25° C. and the acetonitrile was slowly removed at roomtemperature to obtain a white solid of the desired silver2-hydroxyisobutyrate pyridine complex as confirmed by ¹H NMR (CD₃CN) δ8.56 (m, 2H), 7.8 (m, 1H), 7.4 (m. 2H), 1.40 (s, 6H).

I-5: Preparation of Silver 2-Hydroxyisobutyrate 2,6-DimethylpyridineComplex

To a slurry of silver 2-hydroxyisobutyrate (1.0 g, 4.76 mmol) inacetonitrile (5 ml), 2,6-dimethylpyridine (1.01 g, 9.52 mmol) was addedto obtain a clear reaction solution that was then stirred for additional10-15 minutes at 25° C. and the acetonitrile was slowly removed at roomtemperature to obtain a white solid of the desired silver2-hydroxyisobutyrate pyridine complex as confirmed by ¹H NMR (CD₃CN) δ7.6 (m, 1H), 6.9 (m, 2H), 2.5 (s 6H), 1.40 (s, 6H).

I-6: Preparation of Silver 2-Ethyl-2-hydroxybutyrate Pyridine Complex

Silver 2-ethyl-2-hydroxybutyrate was prepared as follows. A solution of50% sodium hydroxide solution (58.8 g; 0.735 moles) is added to 1.05liter chilled (15° C.) deionized (DI) water employing mechanicalstirring and external cooling at 15° C. 2-Ethyl-2-ethyl-2-hydroxybutyricacid (97.02 g; 0.750 moles) was added in portions maintaining theresulting reaction solution temperature near or below ambienttemperature. After this addition, the homogenous mixture is stirred at15° C. for 30 minutes to ensure complete reaction. Silver nitrate (127.4g; 0.75 mole) in deionized water (187.5 ml) was slowly added to thesodium 2-hydroxyisobutyrate solution over 10 minutes. During theaddition, a precipitate formed. The reaction solution was stirred at 15°C. for 30 minutes, slurry filtered (medium fit size 90), and washedwater (50 ml). The collected solid was further washed with two 200 mlportions of acetone and air dried to provide the desired silver2-ethyl-2-hydroxybutyrate product at 60% yield.

To a slurry of silver 2-ethyl-2-hydroxybutyrate (1.0 g, 4.18 mmol) inacetonitrile (5 ml), pyridine (0.661 g, 8.37 mmol) was added and thereaction solution was stirred at 25° C. for 10 minutes. The acetonitrilewas slowly removed at room temperature to obtain a white solid of thedesired silver 2-ethyl-2-hydroxyisobutyrate pyridine complex having thecrystal structure shown in FIG. 3 as confirmed by ¹H NMR (CD₃CN).

I-7: Preparation of Silver 2-Hydroxyisobutyrate Oxazole Complex

To a slurry of silver 2-hydroxyisobutyrate (1.0 g, 4.76 mmol) inacetonitrile (4 ml), oxazole (0.50 g, 19.2 mmol) was added to obtain aclear reaction solution. The reaction solution was stirred at 25° C. for10 minutes to obtain the desired silver 2-hydroxyisobutyrate oxazolecomplex as confirmed by H NMR (CD₃CN) δ 8.08 (s, 1H), 7.90 (s, 1H), 7.21(s. 1H), 1.2 (s, 6H).

I-8: Preparation of Silver Lactate 3-Fluoropyridine Complex

To a slurry of silver lactate (1.0 g, 5.08 mmol) in acetonitrile (5 ml),3-fluoropyridine (1.97 g, 20.3 mmol) was added to obtain a clearreaction solution that was stirred at 25° C. for 10 minutes and thedesired silver lactate 3-fluoropyridine complex was characterized by 1HNMR (CD₃CN) δ 8.27 (d, 1H), 8.39 (d, 1H), 7.46 (d. 1H), 7.30 (d 1H), 4(q, 1H), 1.35 (d, 3H).

I-9: Preparation of Silver 2-Hydroxyisobutyrate 3-Fluoropyridine Complex

To a slurry of silver 2-hydroxyisobutyrate (1.0 g, 4.18 mmol) inacetonitrile (5 ml), 3-fluoropyridine (1.62 g, 16.72 mmol) was added toobtain a clear reaction solution that was stirred at 25° C. for 10minutes to obtain the desired silver 2-hydroxyisobutyrate3-fluoropyridine complex, the structure of which was confirmed by NMR(CD₃CN) δ 8.25 (d, 1H), 8.35 (d, 1H), 7.4 (d. 1H), 7.3 (d 1H), 1.35 (d,6H).

I-10: Preparation of Silver 2-Hydroxyisobutyrate 2-MethylpyrimidineComplex

To a slurry of silver 2-hydroxyisobutyrate (1.0 g, 4.76 mmol) inacetonitrile (4 ml), 2-methylpyrimidine (1.8 g, 19.2 mmol) was added toobtain a clear reaction solution that was stirred at 25° C. for 10minutes to obtain the desired silver 2-hydroxyisobutyrate2-methylpyrimidine complex the structure of which was confirmed by ¹HNMR analysis.

I-11: Electrochemical Characterization of Silver-Ion Complexes

The electrochemical properties of various silver-containing complexes asdefined above using formula (I) were assessed by the common method ofcyclic voltammetry as described for example in “Electrochemical Methods,Fundamentals and Applications,” A. Bard and L. Faulkner (Editors), JohnWiley & Sons, Inc. NY (1980). In this method, each complex was dissolvedat a concentration of about 1 to about 5 mmol in acetonitrile solventcontaining 0.1 molar tetrabutylammonium-tetrafluoroborate as anelectrolyte. Cyclic voltammetry was performed in a two-compartment glasscell equipped with a glassy carbon working electrode, a platinum counterelectrode, and a saturated calomel (SCE) reference electrode. The SCEwas separated from the main compartment of the cell by a salt bridgefilled with 0.1 molar tetrabutylammonium-tetrafluoroborate electrolyte.The glassy carbon electrode was polished using 1 μm alumina paste priorto each voltammetric scan. Measurements were conducted at 25° C. using apotential sweep rate of 0.1 V/sec.

A typical cyclic voltammogram of the silver 2-hydroxyisobutyratepyridine complex prepared as shown above is shown in FIG. 4 wherein, theelectrode potential is cycled between the limits of −0.5 V and +2.0 Vstarting in a negative-going direction from an initial potential of +0.5V. Three electrochemically active regions were identified. The observedcurrent “wave” in the negative potential region from +0.1 V to −0.5 V isassociated with the electrochemical reduction of the silverion-containing complex. This reduction process results in the plating ofsilver metal onto the carbon electrode. The sharp current wave observedin the positive potential region from +0.1 V to +0.5 V corresponds tothe oxidation of the plated silver metal to form a soluble silver ion.The sharp symmetrical shape of the latter electrochemical oxidation waveis fully consistent with the oxidation dissolution (“stripping”) ofsilver metal from the electrode surface. Finally, a third, broadelectrochemical wave in the positive potential region from about +1.0 Vto +2.0 V is assigned to the overlapping oxidation waves of theincorporated component parts (“P” and “L”) of the complex.

Cyclic voltammograms for other complexes of formula (I) are very similarto that of FIG. 4 peak potentials for the reduction and oxidation ofvarious complexes are shown in TABLE III below. Oxidation potentialsdetermined for the individual α-oxy carboxylate components determined bythe experimental method described above are shown in the following TABLEIV. Oxidation potentials for primary alkylamines are found for examplein Adenier et al., Langmuir, 2004, Vol. 20, pp. 8243-8253.

TABLE III Voltammetry Results for (Ag⁺)_(a)(L)_(b)(P)_(c) inAcetonitrile Reduction Oxidation peak peak Complex L P StructurePotential Potential C-1 iso-butyl acetate pyridine

 −0.27 V +1.07 V I-1 lactate 2,6- dimethyl pyridine

 −0.21 V +1.32 V I-4 hydroxy isobutyl- rate pyridine

+0.017 V +1.13 V lactate pyridine

+0.064 V +1.21 V

TABLE IV Voltammetry Results for Carboxylate Components in AcetonitrileOxidation L Peak Potential lactate +1.1 V acetate +1.27 V

I-12: Preparation of Silver 2-Methoxyisobutyrate-Pyridine Complex

2-Methoxyisobutyric acid was synthesized as follows. A solution ofmethyl 2-hydroxyisobutyrate (2.0 g, 16.93 mmol) in N,N-dimethylformamide(20 ml) at 0° C. was treated with NaH (60% in mineral oil, 0.813 g,20.33 mmol), stirred for 30 minutes at 0° C., treated with iodomethane(1.269 ml, 20.29 mmol), allowed to warm to room temperature, and stirredovernight. The resulting solution was diluted with ethyl acetate,quenched with cold saturated ammonium chloride, and extracted with ethylacetate three times, and the combined organic extractions were washedwith saturated NaHCO₃, 10% lithium chloride, and sodium chloride, driedover sodium sulfate, and concentrated to dryness to afford 2-methoxyiso-butyrate sodium salt (2.08 g, 93% yield) as characterized by ¹H NMR(400 MHz, DMSO-d₆): δ 3.64 (s, 3H), 3.11 (s, 3H), 1.30 (s, 6H).2-Methoxy iso-butyrate silver salt was obtained by the following methoddescribed above in Inventive Example 6.

Silver 2-methoxyisobutyrate pyridine complex was then prepared asfollows. To a slurry of silver 2-methoxy-isobutyrate as described above(1 g, 4.76 mmol) in acetonitrile (4 ml), pyridine (1.8 g, ˜23 mmol) wasadded to obtain a clear reaction solution that was stirred at 25° C. for10 minutes to obtain the desired silver 2-methoxyisobutyrate pyridinecomplex as confirmed by NMR analysis.

I-13: Preparation of Silver Pyruvate Pyridine Complex

To a solution of pyruvic acid (1.0 g, 11.36 mmol) in acetonitrile (4ml), pyridine (1.8 g, 23 mmol) was added followed by addition of silvernitrate (1.93 g, 11.37 mmol). The resulting reaction solution wasstirred at 25° C. for 10 minutes to obtain the desired silver pyruvatepyridine complex as confirmed by ¹H NMR.

I-14: Preparation of Silver 3-Methyl-2-oxobutanate Pyridine Complex

To a solution of 3-methyl-2-oxobutanoic acid (1.0 g, 8.62 mmol) inacetonitrile (4 ml), pyridine 1.5 g, 18 mmol) was added followed byaddition of silver nitrate (1.46 g, 8.62 mmol). The resulting reactionsolution was stirred at 25° C. for 10 minutes to obtain the desiredsilver 3-methyl-2-oxobutanate pyridine complex as confirmed by ¹H NMR.

I-15: Preparation of Silver Lactate 4-Methylpyrimidine Complex

To a slurry of silver lactate (1.0 g, 5.1 mmol) in acetonitrile (4 ml),oxazole (1.84 g, 20.2 mmol) was added to obtain a clear reactionsolution that was stirred at 25° C. for 10 minutes to obtain the desiredsilver lactate 4-methylpyrimidine complex as confirmed by ¹H NMR (CD₃CN)δ 9.06 (s, 1H), 8.61 (d, 1H), 7.37 (d. 1H), 4 (q, 1H), 2.54 (s, 3H),1.35 (d, 3H).

Invention Example 1: Thermal Generation of Conductive Silver Metal Using2-Hydroxyisobutyrate Pyridine Complex and Hydroxypropyl Cellulose

This example demonstrates the thermal generation of anelectrically-conductive silver-containing coating in a product articleusing a non-aqueous precursor composition according to the presentinvention.

The silver 2-hydroxyisobutyrate pyridine complex described above as I-4(0.4 g) was dissolved in acetonitrile (1 ml). Hydroxypropyl cellulose(0.005 g; 1.2 weight %, or 4 weight % based on the total weight of thereducible silver ions) was added and dissolved to form the desirednon-aqueous precursor composition at room temperature. This compositionwas spin coated on a glass plate at 1000 rpm and then placed on a hotplate set at 150° C. for 3-5 minutes and cooled to room temperature. Theresistivity of the resulting thermally cured coating was measured usinga 4-point probe device and found to be 1-2Ω/□. The heating temperaturewas decided using thermal gravimetric analysis (TGA) of silver2-hydroxyisobutyrate-pyridine complex (see FIG. 5) which shows that theonset of thermal decomposition of complex begins near 125° C. and it iscomplete at 150° C. The surface area of the thermally cured coating was1 cm² and its thickness was about 100 nm. The surface morphology and thethickness of the silver-containing film was observed by scanningelectron microscopy (SEM). Adhesion of the silver-containing coating toa glass substrate was found to be good as measured by adhesive tapetest.

Inventive Example 2: Printing and Thermal Generation of ConductiveSilver Metal Using 2-Hydroxyisobutyrate Pyridine Complex andHydroxypropyl Cellulose

A flexographic printing plate was obtained from a commercially availableKodak Flexcel NX photopolymer plate (precursor) using a flexographic IGTF1 printer. A relief image was provided by imaging the photopolymerplate through a mask that was written using the Kodak Square Spot lasertechnology at a resolution of 12,800 dpi. Test patterns of thenon-aqueous precursor composition described above in Invention Example 1were printed onto a glass substrate to provide a precursor article withthermally-sensitive thin film patterns. The precursor article was heatedat 150° C. for 3-5 minutes to obtain a silver metal-containing film thatwas determined to have a sheet resistivity in the product article of1-2Ω/□. Adhesion of the silver-containing coating to the glass substratewas found to be good as measured by an adhesive tape test.

Invention Example 3: Thermal Generation of Conductive Silver Metal Using2-Hydroxyisobutyrate Pyridine Complex and Poly(Vinyl Acetate)

This example demonstrates the thermal generation of anelectrically-conductive silver-containing coating in a product articleusing a non-aqueous precursor composition according to the presentinvention.

The silver 2-hydroxyisobutyrate pyridine complex described above as I-4(1.54 g) was dissolved in acetonitrile (2 ml). Poly(vinyl acetate) (0.04g; 2.5 weight %, or 9 weight % based on the total weight of reduciblesilver ions) was added and dissolved to form the desired non-aqueousprecursor composition at room temperature. This composition was spincoated on a glass plate at 1000 rpm and then placed on a hot plate setat 150° C. for heating at 150° C. for 3-5 minutes. It was then cooled toroom temperature and its sheet resistivity was measured using 4-pointprobe device to be 0.6Ω/□. The area of the silver-containing coating was1 cm² and its thickness was about 100 nm. The surface morphology and thethickness of the silver-containing film in the product article wasobserved by scanning electron microscopy (SEM) and adhesion of thesilver-containing coating to the glass substrate was found to be good asmeasured by an adhesive tape test.

Invention Example 4: Thermal Generation of Conductive Silver Metal Using2-Hydroxyisobutyrate Pyridine Complex and Poly(MethylMethacrylate-Co-Hydroxyethyl Acrylate)

This example demonstrates the thermal generation of anelectrically-conductive silver coating in a product article using anon-aqueous precursor composition according to the present invention.

The silver 2-hydroxyisobutyrate pyridine complex described above as I-4(0.6 g) was dissolved in acetonitrile (1 ml). Poly(methylmethacrylate-co-hydroxyethyl acrylate) (0.002 g; 0.33 weight %, or 1.1weight % based on the total weight of reducible silver ions) was addedand dissolved to form the desired non-aqueous precursor composition atroom temperature. This composition was spin coated on a glass plate at1000 rpm and then placed on a hot plate set at 150° C. The compositionwas heated at 150° C. for 3-5 minutes and then cooled to roomtemperature. The sheet resistivity of the resulting thermally-curedcoating was measured using 4-point probe device and found to be 1-2Ω/□.The area of the coating was 1 cm² and its thickness was about 100 nm.The surface morphology and the thickness of the silver-containing filmwas observed by scanning electron microscopy (SEM). Its adhesion to aglass substrate was found to be good as measured by an adhesive tapetest.

Invention Example 5: Thermal Generation of Conductive Silver Metal Using2-Hydroxyisobutyrate Pyridine Complex and Poly(MethylMethacrylate-Co-2-Chloroethyl Methacrylate-Co-Hydroxyethyl Methacrylate)

This example demonstrates the thermal generation of anelectrically-conductive silver-containing coating using a non-aqueousprecursor composition according to the present invention.

The silver 2-hydroxyisobutyrate pyridine complex described above as I-4(1.54 g) was dissolved in acetonitrile (2 ml). Poly(methylmetacrylate-co-2-chloroethyl methacrylate-co-hydroxyethyl methacrylate)(0.04 g; 2.5 weight %, or 9 weight % based on the total weight ofreducible silver ions) was added and dissolved to form the desirednon-aqueous precursor composition at room temperature. This compositionwas spin coated on a glass plate at 1000 rpm and then placed on a hotplate set at 150° C. The coating was heated at 150° C. for 3 minutes andthen cooled to room temperature. Its sheet resistivity was measuredusing 4-point probe device and found to be 0.6Ω/□. The area of thecoating was 1 cm² and its thickness was about 100 nm. The surfacemorphology and the thickness of the silver-containing film was observedby scanning electron microscopy (SEM) and its adhesion to the glasssubstrate was found to be good as measured by adhesive tape test.

The invention has been described in detail with particular reference tocertain preferred embodiments thereof, but it will be understood thatvariations and modifications can be effected within the spirit and scopeof the invention.

The invention claimed is:
 1. A non-aqueous precursor compositionconsisting essentially of: (a) a silver complex comprising one or morereducible silver ions that are present in an amount of at least 30weight % and up to and including 90 weight %, based on the total weightof the non-aqueous precursor composition, which one or more reduciblesilver ions are complexed with an α-oxy carboxylate and a 5- or6-membered N-heteroaromatic compound, the silver complex beingrepresented by the following formula (I):(Ag⁺)_(a)(L)_(b)(P)_(c)   (I) wherein L represents the α-oxycarboxylate; P represents the 5- or 6-membered N-heteroaromaticcompound; a is 1 or 2; b is 1 or 2; and c is 1, 2, 3, or 4, providedthat when a is 1, b is 1, and when a is 2, b is 2; (b) a hydroxy-free,nitrile-containing aprotic solvent having a boiling point at atmosphericpressure of at least 100° C. and less than 500° C.; and (c) a polymerthat is either (i) a hydroxy-containing cellulosic polymer or (ii) anon-cellulosic acrylic polymer having a halo- or hydroxy-containing sidechain, which polymer is present in an amount of at least 0.25 weight %and up to and including 15 weight %, based on the total weight ofreducible silver ions in the silver complex, wherein L is represented bythe following formula (II):

wherein R₁, R₂ and R₃ are independently hydrogen or branched or linearalkyl groups, or by the following formula (III):

wherein R₄ is a branched or linear alkyl group having 1 to 8 carbonatoms and any of the hydrogen atoms in the R₄ branched or linear alkylgroup optionally can be replaced with a fluorine atom, and P is selectedfrom the group consisting of pyridine, 2-methylpyridine,4-methylpyridine, 2,6-dimethylpyridine, 2,3-dimethylpyridine,3,4-dimethylpyridine, 4-pyridylacetone, 3-chloropyridine,3-fluoropyridine, oxazole, 4-methyloxazole, isoxazole,3-methylisoxazole, pyrimidine, pyrazine, pyridazine, and thiazole. 2.The non-aqueous precursor composition of claim 1, wherein the (i)hydroxy-containing cellulosic polymer is selected from the groupconsisting of hydroxypropyl methylcellulose, hydroxypropyl cellulose,hydroxyethyl cellulose, and mixtures thereof.
 3. The non-aqueousprecursor composition of claim 1, wherein the (ii) non-cellulosicacrylic polymer comprises recurring units derived from one or more(meth)acrylates, at least one of which (meth)acrylates comprises a halo-or hydroxy-containing side chain.
 4. The non-aqueous precursorcomposition of claim 1, wherein the (i) or (ii) polymer is present in anamount of at least 2 weight % and up to and including 15 weight %, basedon the total weight of reducible silver ions in the silver complex. 5.The non-aqueous precursor composition of claim 1, wherein thehydroxy-free, nitrile-containing aprotic solvent is acetonitrile,benzonitrile, butyronitrile, propionitrile, isovaleronitrile, orvaleronitrile or a mixture of two or more of these.
 6. The non-aqueousprecursor composition of claim 1, wherein: the hydroxy-free,nitrile-containing aprotic solvent is acetonitrile; P is selected fromthe group consisting of pyridine, 2-methylpyridine, 4-methylpyridine,2,6-dimethylpyridine, 2,3-dimethylpyridine, 3,4-dimethylpyridine,3-chloropyridine, and 3-fluoropyridine; and the (c) polymer ishydroxypropylmethyl cellulose.
 7. The non-aqueous precursor compositionof claim 1, wherein R₁ is hydrogen or a branched or linear alkyl grouphaving 1 to 3 carbon atoms, and R₂ and R₃ are independently branched orlinear alkyl groups having 1 to 8 carbon atoms, wherein any of thehydrogen atoms in the R₁, R₂, and R₃ branched or linear alkyl groupsoptionally can be replaced with a fluorine atom.
 8. The non-aqueousprecursor composition of claim 1, wherein a and b are both 1 and c is 1or
 2. 9. The non-aqueous precursor composition of claim 1, comprisingtwo or more different silver complexes, each represented by formula (I).10. The non-aqueous precursor composition of claim 1, having long termstability such that, when it is held at ambient temperature and underyellow safelight for 24 hours, less than 0.1 mol % of its originalsilver ion content is reduced to silver metal.
 11. The non-aqueousprecursor composition of claim 1, comprising no more than 5 weight %based on the total weight of the hydroxy-free, nitrile-containingaprotic solvent.